The invention relates to a hydraulic control arrangement.
A hydraulic control arrangement known, for example, from DE 196 19 860 A1. This document describes a hydraulic control arrangement which is used on a die-casting machine and in which a directional control valve is used to shut off a load line leading from the latter to a pressure space of a hydraulic cylinder, to connect it to a discharge line leading to a tank or connect it to an inlet line. The inlet line is fed by a hydraulic pump which draws pressure medium from the tank. Arranged in the inlet line is a two-way cartridge valve designed as a seat valve, which allows a first inlet line section running between the hydraulic pump and the two-way cartridge valve to be isolated from a second inlet line section leading off from the two-way cartridge valve to the directional control valve. When the control piston of the two-way cartridge valve is seated on its seat, the two inlet line sections are isolated from one another. The valve used is a conventional two-way cartridge valve with a directional control function, the control piston of which has two opening surfaces acting in the opening direction, one of which is situated centrally on the control piston, corresponds in diameter to the seat diameter and is exposed to the pressure in the second inlet line section. The second opening surface is an annular surface, the inside diameter of which corresponds to the seat diameter and the outside diameter of which corresponds to the guiding diameter of the control piston and which can be subjected to the pressure in the first inlet line section. On the control piston there is also a closing surface which acts in the closing direction and which is exposed to the pressure in a rearward control space of the two-way cartridge valve. Together, the two opening surfaces are as large as the closing surface.
In a rest position, which it assumes under the action of a compression spring, a pilot valve connects the rearward control space to the first inlet line section. In this position of the pilot valve, the two-way cartridge valve, the control piston of which is usually additionally acted upon in the closing direction by a spring, cannot be opened by the pressure in the first inlet line section and by the pressure in the second inlet line section, which is normally not greater than the pressure in the first inlet line section. By energizing an electromagnet, the pilot valve can be switched to a position in which it connects the rearward control space at the control piston to the tank. The pressure prevailing in the first inlet line section and acting on the annular surface of the control piston can now raise the control piston from the seat against the, generally weak, closing spring and open the two-way cartridge valve.
It is possible to implement an emergency off facility with the valve described. In normal operation, the electromagnet of the pilot valve is excited and the two-way cartridge valve is open. If an emergency occurs, an electric switch can be actuated, for example, interrupting the power supply to the electrical systems, with the result that the electromagnet of the pilot valve is also separated from the power supply. The pilot valve moves into its rest position by virtue of the compression spring and connects the rearward control space at the control piston to the first inlet line section, with the result that the two-way cartridge valve closes and interrupts the flow of pressure medium to the directional control valve in a leak-free manner.
DE 44 20 459 A1 has disclosed a hydraulic control arrangement, based on the load-sensing principle, which, for emergencies, likewise has a valve by means of which a second inlet line section can be isolated from a first inlet line section. The isolating valve, which can be controlled by means of an electromagnetically actuable pilot valve, is clearly a spool valve which, in the rest position of the pilot valve, not only separates the two inlet line sections from one another but also connects the load-indicating line to the tank and hence relieves it. The pressure in the second inlet line section is also dissipated via the load-indicating line if the load-sensing directional control valve is in a working position to the side of its central position in which there is an aperture cross section between the second inlet line section and the load-indicating line.
DE 43 24 177 A1 has disclosed a hydraulic control arrangement, based on the load-sensing principle, in which, after an emergency-off signal has been triggered, an isolating valve isolates two inlet line sections from one another, shuts off the load-indicating line and connects a load-indicating port on the regulator of the variable-displacement pump to the tank. The isolating valve is again a spool valve.